The susceptibility of individuals to chemicals and environmental hazards at the extremes of the population age-distribution is often not adequately assessed. By understanding genes expressed at the various life stages, the assessment of health risk can be more rationally determined. Children and older adults may be more susceptible to chemicals compared to adults because of differences is physiology, pharmacokinetics, and pharmacodynamics. Genetic and epigenetic changes that occur with age and chemical exposure may also alter susceptibility to chemicals. This session examines the genomic and epigenomic changes that occur with age in the rat liver and kidney. Human relevance will be addressed using data from human studies, including a longitudinal birth cohort study in Mexican-American children exposed to pesticides and a cohort of older men from the Normative Aging Study exposed to particulate matter. Ultimately, understanding the implications of genetic and epigenetic changes related to age on the effects of chemical exposure will help to better assess the impacts of environmental exposures on the health of children and older adults.